The present invention relates to a system for exciting electrodeless lamps with microwave electromagnetic radiation. Specifically, a compact microwave frequency power source is coupled to an electrodeless lamp with a minimum of waveguide structure or coupling devices.
Microwave powered electrodeless lamps have been used in various industrial processes for generating ultraviolet light used to cure materials and/or in other manufacturing processes. The electrodeless lamps have the desirable characteristic of a long life, with unchanging light spectrum, as well as a high-intensity light output. These lamps are excited by microwave energy generated by a magnetron which was originally intended for use in microwave ovens. The conventional microwave generating magnetrons include an output antenna which is coupled via a waveguide structure and perhaps an isolator to such an oven or to an electrodeless lamp which terminates one end of the microwave waveguide structure.
Applications for the electrodeless lamp outside the industrial processing technologies are currently being developed. One application requiring a high intensity visible light source includes projection television systems. In these systems, a source of white light is filtered into the primary red, green and blue colors. The separated colors are modulated by a light valve panel with a video signal representing the red, green and blue content of a video image. The modulated monochrome images are recombined in a dichroic mirror structure to form a single color image. The resulting color image is projected to a display screen using a projection lens.
These consumer applications for electrodeless lamps impose space and weight limitations not found in the earlier industrial applications on the light source. Hence, it is desirable to provide for coupling of the lamp to a microwave source with a minimal amount of microwave waveguide structure and/or coupling devices such as isolators, which burden the system with their weight and size requirements.
In order to derive the required light output from the electrodeless lamps, it is necessary to match substantially the impedance presented by the electrodeless lamp to the output of the magnetron power source. The need to remove the size and weight imposed by the waveguide structures and coupling devices of the prior art is accompanied by a need to maintain the impedance match between the electrodeless lamp and microwave source. Any substantial mismatch will not only deliver less power to the electrodeless lamp, which is converted to luminant energy, but will also create standing waves which, depending upon their phase, can shift the frequency of the magnetron source, further mismatching the electrodeless lamp to the source, and commensurately reducing the available light output.